1. Field of the Invention
The present invention relates to a power transmission arrangement in a working vehicle with a working unit such as a cultivating unit and mower unit attached thereto, and a transmission for the working vehicle.
2. Related Art
In a vehicle equipped with a working unit such as a bucket, cultivating unit and mower unit on the front side, rear side and/or below the lengthwise center of a chassis, driving power from a driving power source must be divided into a running power transmission path and a driving power transmission path for working unit so as to be transmitted to driving wheels and the working unit. This poses a problem of increasing a size of the transmission in the vehicle.
For example, Japanese Patent Application Publication No. Hei-01-17883 and Utility Model Application Publication No. Hei-01-37298 disclose arrangements, which are applicable to the vehicle of the above type, for downsizing the size of the transmission.
The transmission disclosed in each of the above-cited publications has an input shaft for the working unit (PTO input shaft) and a running power input shaft, which are respectively aligned in vertical and parallel relationship with each other, and a transmission case in which the power transmission path for working unit and the running power transmission path are arranged respectively closer to upper and lower sides thereof with occupation of spaces as much compact as possible in an attempt to reduce the size of the transmission.
Meanwhile, for the vehicle equipped with a working unit as mentioned above, a hydraulic power unit for operating the working unit must be provided in some cases, in addition to a power-take-off arrangement for taking off driving power for the working unit. As such a hydraulic power unit, it can be cited a hydraulic lift unit for lifting a cultivating unit mounted on the rear side of the chassis.
As described above, in each of the above-cited publications, although the downsizing of the transmission may be achieved by arranging the running power transmission path and the power transmission path for working unit within the transmission case respectively closer to the upper and lower sides thereof with occupation of spaces as much compact as possible, such downsizing was not considered for the transmission of the vehicle provided with the aforesaid hydraulic power unit.
Specifically, in a vehicle disclosed in each of the cited publications, a hydraulic power unit for reciprocating a cultivating unit or any other working unit is disposed on a top surface of the transmission, while a hydraulic pump for feeding pressurized fluid to the hydraulic power unit is supported on a rear wall of the transmission case.
More specifically, in the transmission described in each publication, a clutch shaft and an intermediate shaft, which constitute a part of the power transmission path for working unit (PTO system), extend below and on the opposite lateral sides of a PTO input shaft, so that an upper space of the transmission case is occupied by this PTO power transmission path. Accordingly, in this conventional transmission, it is not possible to secure within the transmission case closer to the upper side a space for accommodating the hydraulic pump for feeding pressurized fluid to the hydraulic power unit, a driving power transmission mechanism for the hydraulic pump, etc. For these reasons, the conventional transmission has the hydraulic pump supported on the rear wall of the transmission case and a rear end of the PTO input shaft extending through the rear wall of the transmission case, through which the hydraulic pump is driven.
Thus, for the vehicle equipped with the hydraulic pump, the hydraulic pump of the conventional transmission extending rearwards through the transmission case poses a difficulty in shortening the length of the transmission with the hydraulic pump.
Also, according to the above arrangement, working fluid reserved in the transmission case for the hydraulic power unit is once transmitted around the rear side of the transmission case and then to the upper side of the transmission case. Accordingly, a hydraulic fluid circulation path to the hydraulic power unit must be elongated, which necessitates application of an excessive load to the hydraulic pump.
As another disadvantage involved in the vehicle described in each cited publication, since the hydraulic power unit is disposed on the top surface of the transmission case, a higher position must be prepared for mounting of the hydraulic power unit. This arrangement poses a problem of increasing an vehicle height. Since a driving seat is above the hydraulic power unit in a general arrangement, this invites a difficulty for a driver to get on and off the seat.
As described above, the power transmission path for working unit of the conventional transmission is entirely located in the upper space of the transmission case. On the other hand, a mid-PTO shaft for driving a mid-mount more or the like is located in the lower space of the transmission case. Accordingly, a power transmission mechanism between the PTO input shaft and the mid-PTO shaft in the conventional transmission must be formed throughout the entire region of the transmission case along the vertical direction. This poses a problem of necessitating a complicated structure for the transmission mechanism.
The present invention was conceived in light of those conventional techniques. It is an object of the present invention to provide a transmission with the power transmission path for working unit and the running power transmission path, which is capable of achieving downsizing of the transmission case, as well as effectively securing a space for accommodating parts for the hydraulic lift unit or the like within the transmission case.
It is another object of the present invention to provide a power transmission arrangement in a vehicle provided with a working unit operable by a hydraulic power unit, which is capable of shortening a hydraulic fluid distribution path to the hydraulic power unit.
It is still another object of the present invention to provide a power transmission arrangement in a vehicle provided with a working unit operable by a hydraulic power unit, which is capable of stably supporting a cylinder tube of the hydraulic power unit at a lower position.
To achieve the above objects, there is provided a transmission for a working vehicle, which includes:
a transmission case providing an accommodation space therein for accommodating a differential gear unit as locating the same substantially below a lengthwise center of the transmission case, in which driving power with its speed changed from an engine is divided and transmitted right and left driving axles through the differential gear unit;
a PTO input shaft supported by the transmission case for receiving the driving power from the engine;
a running power input shaft supported by the transmission case for receiving the driving power from the engine via a transmission unit;
the PTO input shaft located with its rotational axis extending in a vehicle lengthwise direction substantially at a widthwise center of the transmission case along a vehicle width direction;
the running power input shaft located with its rotational axis extending in the vehicle lengthwise direction substantially at the same position as that of the PTO input shaft along the vehicle width direction and at a lower side of the PTO input shaft; and wherein
the accommodation space for accommodating the differential gear unit is displaced to a first lateral side of the vehicle along the vehicle width direction, a running power transmission shaft is located on the front side of the space with its axis extending in the vehicle lengthwise direction, and the running power input shaft, the running power transmission shaft and the differential gear unit are interlocked to each other via a running power gear train;
a mid-PTO shaft having a front end protruding forwards through the transmission case, the mid-PTO shaft located within the transmission case closer to a second lateral side of the transmission case along the vehicle width direction and lower side of the transmission case with its axis extending in the vehicle lengthwise direction and its rear end reaching to a rear side of the transmission case;
a PTO power transmission shaft interlocked with the PTO input shaft via a main PTO gear train located on the front side of the transmission case, the PTO power transmission shaft located within the transmission case closer to the second lateral side along the vehicle width direction with its axis extending in the vehicle lengthwise direction and its rear end reaching to the rear side of the transmission case; and
a mid-PTO gear train located within the transmission case closer to a rear side thereof for interlocking the PTO power transmission shaft with the mid-PTO power transmission shaft.
With the transmission having the above arrangement, it is possible to prevent increase in size of the transmission case, while providing within the transmission case a free space on the upper side of a running power transmission path. This free space may be utilized for example to accommodate constitutional parts of a hydraulic lift unit.
In addition, since the mid-PTO gear train is located within the transmission case closer to the rear side thereof, a distal end of the mid-PTO shaft, which is driven through the mid-PTO gear train can be positioned as close as possible to the driving axle. Accordingly, it is possible to provide a power transmission mechanism for connection between the mid-PTO shaft and the working unit driven by the mid-PTO shaft with an improved durability and noise prevention arrangement.
In the above arrangement, the PTO power transmission shaft and the mid-PTO shaft are displaced to the same lateral side along the vehicle width direction within the transmission case so as to position both the shafts as close as possible to each other. This can simplify a power transmission arrangement between both the shafts.
According to a preferable arrangement, the PTO power transmission shaft and the mid-PTO power transmission shaft are respectively located above and below the driving axles.
According to another preferable arrangement, the transmission further includes a rear PTO shaft having a rear end protruding rearwards through the transmission case located substantially at the widthwise center of the transmission case along the vehicle width direction and above the PTO power transmission shaft; and a rear PTO gear train for interlocking the PTO power transmission shaft with the rear PTO shaft having at least a part located closer to the first lateral side of the transmission case along the vehicle width direction than the PTO power transmission shaft is.
According to a still preferable arrangement, the transmission further includes a switching unit for selectively switching on/off power transmission from the PTO power transmission shaft to at least one of the mid-PTO gear train and the rear PTO gear train.
According to another aspect of the present invention, there is provided a power transmission arrangement in a working vehicle with a working unit mounted thereto, which includes:
an input shaft supported by a transmission case for receiving driving power for driving the working unit from a driving source;
a hydraulic power unit for the working unit and a valve unit for controlling feeding and discharging of pressurized fluid for the hydraulic power unit are connected with each other along a vehicle lengthwise direction within the transmission case closer to an upper side thereof or on a top surface of the transmission case, and closer to a first lateral side of the transmission case along the vehicle width direction;
a hydraulic pump driven through the input shaft is located closer to a second lateral side along the vehicle width direction than the hydraulic power unit and the valve unit are;
a fluid distribution path is arranged so that hydraulic fluid reserved within the transmission case is drawn around a lower side of the hydraulic pump and then fed into the hydraulic pump through a suction port thereof; and
the hydraulic pump has a discharge port connected with a suction port of the valve unit.
With the aforesaid power transmission arrangement, it is possible to shorten a hydraulic fluid distribution path to the hydraulic power unit, and hence achieves downsizing of the hydraulic pump, downsizing of the vehicle and improved response rate of the hydraulic power unit.
According to a preferable arrangement, the power transmission arrangement further includes a filter located within the transmission case closer to a lower side thereof and substantially at the same position as that of the hydraulic pump with respect to the vehicle lengthwise direction; and the fluid distribution path arranged so that the hydraulic fluid reserved within the transmission case is fed into the suction port of the hydraulic pump through the filter.
According to still another aspect of the present invention, there is provided a power transmission arrangement in a working vehicle with a working unit mounted thereto in such a manner as to be vertically movable through a lift arm, which includes:
an input shaft for receiving driving power for driving the working unit from a driving source supported by a transmission case with a first bulging portion upwardly bulging at a position closer to a first lateral side of the transmission case along a vehicle width direction;
a hydraulic power unit for the working unit including a cylinder tube extending in a vehicle lengthwise direction, a piston reciprocably and fluid-tightly mounted within the cylinder tube and a supporting shaft operatively connected with the piston in such a manner as to be rotatable around its axis based upon reciprocal movement of the piston, in which the cylinder tube is located within a space defined by the first bulging portion, and the supporting shaft is supported by the transmission case so as to extend along the vehicle width direction and have at least one of first and second ends extending to the outside of the transmission case to form an outer extension, with which the lift arm is connected;
a hydraulic pump for feeding pressurized fluid into the hydraulic power unit located on a top surface of the transmission case closer to a second lateral side along the vehicle width direction than the first bulging portion is; and
the input shaft being arranged so that driving power for the hydraulic pump is taken off therethrough.
With the aforesaid power transmission arrangement, it is possible to support the cylinder tube at a lower position, thereby lowering the vehicle height and increasing an operational efficiency of the hydraulic power unit.
According to a preferable arrangement, the transmission case is formed with a second bulging portion upwardly bulging at a position substantially at the same position as that of the hydraulic pump with respect to the vehicle width direction, and the hydraulic pump is supported on the second bulging portion.
According to a more preferable arrangement, the power transmission arrangement further includes at least a drive train extending from the input shaft to the hydraulic pump so that at least a portion thereof is placed within a space defined by the second bulging portion.
According to another preferable arrangement, the power transmission arrangement further includes a valve unit for controlling feeding and discharging of pressurized fluid for the hydraulic power unit connected with the cylinder tube so as to close one of open ends of the cylinder tube, the one of open ends being positioned opposite to another side of the cylinder tube, on which the supporting shaft is located; and a fluid distribution path being arranged so that hydraulic fluid reserved within the transmission case is drawn around a lower side of the hydraulic pump and then fed into the hydraulic pump through a suction port thereof. The hydraulic pump has a discharge port connected with a suction port of the valve unit.
According to still another preferable arrangement, a filter is located within the transmission case closer to a lower side thereof and substantially at the same position as that of the hydraulic pump along the vehicle lengthwise direction; and a fluid distribution path is so arranged that the hydraulic fluid reserved within the transmission case is fed into the suction port of the hydraulic pump through the filter.
According to another aspect of the present invention, there is provided a transmission for a working vehicle with a working unit mounted thereto in such a manner as to be vertically movable by a hydraulic power unit, which includes:
a transmission case designed to be capable of reserving hydraulic fluid therein;
a PTO input shaft supported by the transmission case and operatively connected with a hydraulic pump so as to operatively receive driving power from an engine; and
a running power input shaft supported within the transmission case and operatively connected with a driving axle so as to operatively receive driving power from the engine via an HST; wherein
the hydraulic pump is so designed as to feed pressurized fluid to the HST and the hydraulic power unit;
the transmission case includes a front supporting wall and a rear supporting wall aligned in series along a fore and aft direction of the vehicle to divide an inner space of the transmission case into a front chamber, a middle chamber and a rear chamber; and
a hydraulic fluid distribution path being so arranged that hydraulic fluid returned from the HST and hydraulic fluid returned from the hydraulic power unit respectively flow into the front chamber and the rear chamber, and the hydraulic pump sucks the hydraulic fluid through the middle chamber.
With the above relatively simple arrangement, it is possible to effectively prevent hydraulic fluid, which has been heated to high temperature during circulation and returned from the HST and the hydraulic power unit, from being fed again to the HST and the hydraulic power unit before it is cooled. As a result, it is possible to effectively prevent deterioration in operational efficiency of the hydraulic pump, the HST and the hydraulic power unit.
According to a preferable arrangement, a PTO clutch for switching on/off power transmission from the PTO input shaft on a downstream side of the hydraulic pump along its power transmission path is placed within the front chamber, while a drive train for driving the PTO shaft is placed within the rear chamber. The front chamber is communicated with the rear chamber through an intermediate chamber, in which a PTO power transmission shaft for connection between the PTO clutch and the drive train is placed.
According to a more preferable arrangement, the transmission further includes a brake shaft located on an upstream side of the driving axle along its power transmission path, and a brake mechanism for applying braking force to the brake shaft. The brake shaft and the brake mechanism may be placed within the intermediate chamber. The intermediate chamber is designed to enable hydraulic fluid to flow thereinto from the front chamber and then flow out into the middle chamber. More preferably, the rear chamber is provided with an interior wall for temporarily receiving return fluid from the hydraulic power unit.
According to a still preferable arrangement, the transmission further includes a mechanical transmission unit for stepwisely varying the speed of driving power inputted to the running power input shaft and operatively transmitting the driving power to a driving axle. The mechanical transmission may be placed within the front chamber. An input end of the driving axle is placed within the middle chamber.
According to still another aspect of the present invention, there is provided a transmission for a working vehicle, which includes:
a transmission case that includes a body with its at least one side closer to a first lateral side of the transmission case along a vehicle width direction forming a lateral opening and a side cover for closing the lateral opening, a PTO input shaft supported by the transmission case and operatively connected with an engine, a PTO shaft supported by the transmission case so as to be able to output driving power to the outside of the transmission case, and a PTO power transmission mechanism constituting a driving power transmission path between the PTO input shaft and the PTO shaft, in which:
the PTO power transmission mechanism includes a clutch unit equipped with a hydraulic clutch mechanism capable of selectively transmitting or shutting off the driving power transmission path between the PTO input shaft and the PTO shaft;
the clutch unit includes a hydraulic brake mechanism for applying braking force to a rotational member of the PTO power transmission mechanism during shutting-off of the power transmission path by the hydraulic clutch unit;
the hydraulic brake mechanism includes a pressing member having a proximal end slidably fitted in a cylinder chamber and a distal end adapted to be brought into and released from engaging relationship with the rotational member of the PTO power transmission mechanism, so that the pressing member selectively applies braking force to and release the same from the PTO power transmission mechanism by controlling feeding of pressurized fluid to the cylinder chamber; and
the cylinder chamber is formed in the side cover of the transmission case.
With the above arrangement, the cylinder chamber, which must be fluid tightly sealed, is not formed in the body of the transmission case but in the side cover, thereby omitting the necessity to work the body of the transmission with higher precision and therefore enabling the body to be relatively easily formed by casting.
According to a preferable arrangement, the hydraulic clutch mechanism and the hydraulic brake mechanism are actuated by working fluid fed from a common hydraulic pressure source. The side cover is provided with a working-fluid controlling member for controlling feeding of working fluid to the hydraulic clutch mechanism and the hydraulic brake mechanism and a pressurized-fluid distributor for distributing pressurized fluid into the hydraulic clutch mechanism and the hydraulic brake mechanism.
According to a more preferable arrangement, the working-fluid controlling member and the pressurized-fluid distributor are respectively and detachably attached on outer and inner surfaces of the side cover.